1. Field of the Invention
The present invention relates to a lens driving device of a mobile phone or a tablet terminal loaded with a camera, in particular to a lens driving device for elastically supporting a lens support for retaining a lens (exactly, a lens assembly integrated more than one lens).
2. Description of Related Art
In recent years, a camera unit loaded in a mobile phone or a tablet terminal is high in pixelate, and is also nearly loaded with an automatic focusing function. As a driving manner of a lens system loaded with the automatic focusing function, the lens driving device using a voice coil motor with simple structure is widely adopted.
The lens driving device using the voice coil motor is provided with the lens support for retaining the lens in the central part. The lens driving device is of the following structure, namely an internal thread part for being screwed with an external thread (generally a right thread) on the side of the lens is formed on the inner circumference side of the lens support, and an initial setting focusing position can be simply adjusted by adjusting the lens to the preset focusing positions.
Referring to FIG. 12 to FIG. 18 appropriately, an existing lens driving device is described.
As shown in FIG. 16, as an ordinary automatic focusing camera unit assembled with the lens driving device 10 using the voice coil motor, after an image sensor unit 30 having electronic devices (not shown) such as a driving IC (Integrated Circuit) or optical components such as an IR (Infrared Radiation) filter 32 is mounted on the lower side of the lens driving device 10, the lens 20 are screwed and inserted from the upper side of the lens driving device 10 in the lens support 3 and is adjusted to the preset focusing position (an infinitely great position or more press-in position than an infinitely great position), and the lens 20 are temporarily fixed with the lens support 3.
Then, focusing actions are carried out actually, if no abnormal problems appear on the pictures presenting views in the far-distance side (upper side direction in the figure), the lens 20 are sufficiently fixed on the lens support 3 by using an adhesive.
As shown in FIG. 12 to FIG. 14, in the ordinary lens driving device 10, in order to control the damage caused when the lens 20 are screwed to the minimum limit, the contour part 7d and contour part 2d of an upper spring 7 and a lower spring 2 and arm parts 7f, 2f which are used for connecting an inner contour part 7e with an inner contour part 2e and take the springs to play functions are disposed in an extending direction when rotating along the clockwise direction. Because under the condition of being opposite to the extending direction, the direction becomes a buckling direction when the lens 20 are screwed, and the lens are easily damaged.
A plurality of bending parts 9a are arranged on the magnet yoke 9 so as to be taken as clamping mechanisms for limiting the amounts of movement in the vertical direction. The bending parts 9a are disposed between the outer wall 3e of the thread part 3c of the lens support 3 and the inner circumference surface of the coil 4 so as to play a role of a reverse magnet yoke in improving the magnetic circuit efficiency. The clamping parts 9c of the bending parts 9a and the clamping parts 3f arranged at the mounting positions on the lower side of the coil 4, namely on the inner side of the coil 4, are oppositely arranged so as to limit the maximum amount of movement of the lens 20.
The clamping parts 9c of the magnet yoke 9 and the clamping parts 3f of the lens support 3 are spaced at intervals C when the lens support 3 does not move, the clamping parts 9c of the magnet yoke 9 abut against the clamping parts 3f of the lens support 3 during driving, and thus the state that the interval C is zero is formed, so as to prevent the lens to be moved beyond the limit, and make sure the adjustment of the focusing position is carried out in the range of the interval C.
Moreover, the lens driving device 10 using the voice coil motor is such configured that the lens 20 goes up and down by means of the arms 7f of the upper spring 7 and the lower spring 2 when the lens 20 are driven, the lens 20 are not in contact with other components, and thus the magnetic retardation can be controlled in the minimum extent.
The structure has already been disclosed by Patent Document 1: JP 2012-88434 and Patent Document 2: JP 4966750.
As mentioned above, a plurality of movable components move up and down only by means of the arms 7f of the upper spring 7 and the lower spring 2 but are not in contact with each other, and thus under the condition that the lens 20 are screwed in the thread part 3c of the lens support 3 of the lens driving device 10, the upper spring 7 and the lower spring 2 generate stress in the extending direction when being subjected to a torque effect. Therefore, when the lens 20 are screwed in the thread part 3c, force below 60 gfcm (gram-force centimeter) (about 0.6 cNm) without damaging the upper spring 7 and the lower spring 2 is needed for twisting.
Moreover, recently, relative to a lens driving device 10, the combined application of various lens 20 with different heights or pixel counts taken as a camera assembly is being developed. However, in the range that the upper spring 7 and the lower spring 2 are not damaged and under the low torque (generally about 20-60 gfcm) without loosening during assembling, all combinations of the various lens 20 which are used for forming the external threads and are called mold number of lens barrel parts and used for forming the mold number of the lens support 3 of the internal thread are difficult to specify. Therefore, the clamping mechanism in the rotating direction is used so as to limit the amount of movement of the lens in the rotating direction, so that the upper spring 7 and the lower spring 2 are unlikely to be damaged under the effect of the torque (generally about 100-150 gfcm) that the thread is not damaged.
For example, as shown in FIG. 14, for the purpose that the amount of components is not added and the amount of movement of the lens in the rotating direction (clamping mechanism in the rotating direction) can be limited, the existing side face part 9b for limiting the bending part 9a on the inner side of the magnet yoke 9 in the vertical direction and the positioning guiding part 3b of the coil 4 of the lens support 3 extend towards the side (face) of the bending part 9a respectively, so that the rotating clamping parts 3d are spaced at intervals F on the side faces and on the two sides along the clockwise direction or counterclockwise direction. The side face parts 9b of the bending part 9a on the inner side of the magnet yoke 9 abut against the rotating clamping parts 3d of the lens support 3, and thus the distance between the side face parts 9b of the bending part 9a on the inner side of the magnet yoke 9 and the rotating clamping parts 3d of the lens support 3 is limited to be the interval F, so that the upper spring 7 and the lower spring 2 are not deformed slightly even if stretching or buckling under the effect of the rotation torque generated when the lens 20 are adjusted to be screwed at the focusing positions.
However, in the lens 20 of a generally used mold product, the lens are manufactured by halving the thread part as a half (at 180-degree intervals) structurally, sometimes the thread position divided in a shaping state is slightly offset, or the center shafts are offset, or the torque during assembling exceeds the specification (called as abnormal torques as follows). As shown in FIG. 13, the bending part 9a of the magnet yoke 9 as the clamping mechanism in the rotating direction is located closer to the lower side than the mounting surface 3h of the inner contour part 7a of the upper spring 7, and enters in the middle of the upper-and-lower position of the coil 4. Therefore, under the condition that the rotating clamping parts 3d or side face parts 9b are damaged by sinking or cutting under the effect of abnormal torque, the problem is unlikely to be observed on the opening side (inserting direction of the lens 20 in the figure, namely the direction of the side of the object to be shot).
That is to say, when the rotating clamping parts 3d are damaged by sinking, the condition that the interval F is exceeded appears. Under this condition, the upper spring 7 and the lower spring 2 are also damaged to cause the problem that the characteristics of the lens 20 are worsened or cause the problem that the reliability is reduced after the lens is in the market.
Therefore, in order to prevent the abnormal torque from causing that the characteristic is reduced or the reliability is reduced on the basis that the existing structure is not changed, high-priced upper spring 7 and lower spring 2 with higher twisting force and high allowable stress need to be used in order to improve the rigidity of the upper spring 7 and the lower spring 2.
Moreover, under the condition of image failure caused by initial failure of an optical system inside the lens 20, the image sensor units 30 having the driving IC are partially expensive, and thus partial failures of the image sensor units 30 cannot be processed, only a damaged lens 20 is removed from the lens support 3 of the lens driving device 10 generally, and then another lens for replacing is assembled again.
Particularly when the lens 20 is removed, for the purpose that the lens 20 is rotated in the lifting (floating in the side of the object to be shot) direction (counterclockwise direction) during being disassembled, the center shaft of the external thread part of the lens 20 and the center shaft of the internal thread part of the lens support 3 are offset, and the lens support 3 is tilt, so that the connected upper spring 7 and lower spring 2 are easily damaged under the effect of force subjected in the buckling direction.
Therefore, in the assembling process of the camera assembly, when the lens 20 is inserted, or under the condition that the lens 20 is removed when the lens 20 is repaired, the help of the clamping mechanism in the rotating direction arranged in the lens driving device 10 is needed; moreover, for the purpose that the upper spring 7 and the lower spring 2 or internal components are not damaged, the rotating clamping parts 3d are arranged on the lens support 3 generally, and the lens 20 is retained by utilizing a fixed clamp embedded with the rotating clamping part 3d. 
For example, as shown in FIG. 15, groove-shaped clamping parts 3r are arranged at the rotating clamping parts 11c of a rotation limiting clamp 11 for fixing of the existing lens support 3 between the upper part of the thread part 3c of the lens support 3 and the lower side of the mounting surface 3h of the inner contour part 7e of the spring 7. The rotation limiting clamp 11 includes an opening part 11a inserted with the lens 20, a guiding part 11b for guiding the shape of the lens driving device 10, namely the shape of the magnet yoke 9, and rotating clamping parts 11c embedded with the clamping parts 3r of the lens support 3.
The widths of the rotating clamping parts 11c are formed to be equal to or slightly smaller than the widths of the clamping parts 3r of the lens support 3, the amount of the rotatable movement is far smaller than the interval F of the clamping mechanism in the rotating direction, and the embedding is carried out in the state that the lens is hardly loosened.
Under the condition that the lens 20 is assembled, the guiding part 11b of the rotation limiting clamp 11 is aligned to the shape of the magnet yoke 9, the rotation limiting clamp 11 is mounted on the upper surface of the magnet yoke 9, the clamping parts 3r of the lens support 3 are embedded with the rotating clamping parts 11c, and the state that the lens support 3 is approximately fixed relative to the magnet yoke 9 (lens driving device 10) is formed. The lens 20 is inserted from the opening part 11a of the rotation limiting clamp 11 and screwed for adjusting through the above state, so that the rotating clamping parts 11c of the rotation limiting clamp 11 or the upper spring 7 and the lower spring 2 cannot be damaged under the effect of the abnormal torque, and the lens 20 can be disassembled safely when the lens is screwed for adjusting or the damaged lens 20. Generally, two to four pairs of clamping parts 11c of the rotation limiting clamp 11 and two to four pairs of clamping pars of the lens support 3 are arranged. Moreover, in order to prevent the shaft from being offset when the lens 20 are inserted, preferably more than three pairs of lens are arranged.
However, the rotation limiting clamp 11 is usually made of metals (such as aluminum and the like) with durability, the clamping parts 3r of the lens support 3 made of resin and the rotating clamping parts 11c are not in contact with each other and are difficult to embed when the lens driving device 10 is mounted. Therefore, under the condition that the clamping parts 3r and the rotating clamping parts 11c are worn, the surfaces of the clamping parts 3r may fall down sometimes to generate micro garbage (about 20 microns).
Under the condition of determining the micro garbage generated by the clamping parts 3r partially before leaving the factory, in order to prevent the reliability from being reduced, the micro garbage can be removed, or the adhesive for fixing is used for being fixed with the lens 20 together so as to prevent the garbage from entering the inside or being attached onto other components. However, under the condition that the damaged lens 20 is discovered through image inspection, the lens 20 needs to be replaced, and the lens 20 is removed from the lens driving device 10. When the lens 20 is removed from the lens driving device 10, the micro garbage may come to the side of the thread part 3c, the removed lens 20 is pulled to fall down inside the device and fall on the IR filter 32 or the image sensor 31, or when the replaced new lens 20 is inserted, the micro garbage falls in the device and remains on the IR filter 32 or the image sensor 31, and the condition of defective pixels appears.
Particularly, in recent years, narrow pixel interval of the image sensor 31 is caused by high pixelate, and the micro garbage is also easily attached onto the IR filter 32 or the image to cause defective or abnormal pixels.
The micro garbage attached onto the upper surface of the IR filter 32 or the image sensor 31 may move along with cleaning before leaving the factory sometimes, but the sensor unit 30 is assembled on the lower side of the lens driving device 10 without a gap, and the micro garbage usually remains inside the device. Therefore, after the product is in the market for popularization, the micro garbage may possibly be attached to a light path to cause defective pixels.
Under the condition that the micro garbage is generated, adhesive property needs to be utilized for removing the garbage for additional work, if the micro garbage falls to be closer to the lower side than the thread part 3c due to operation error, or under the condition that the micro garbage enters the inside of the image sensor unit 30, the garbage cannot be removed, and the expensive camera assembly is taken as an inferior-quality product for treatment, so that the rate of finished products is reduced.
Moreover, recently, in order to pursue high pixel and high image quality further, the boundary dimension of the lens driving device 10 needs to be unchanged, and the lens with maximum diameters (called as large-diameter lens) can also be loaded. For example, under the condition that the shape of the lens driving device 10 using the voice coil motor is 8.5*8.5, the thicknesses of the components as forming elements or the gaps among the components setting to be required minimum limit are taken into consideration, the lens 20 in M6.5 dimensions are also restricted.
As shown in section view of FIG. 17 or FIG. 18, under the condition that a circular coil 4 is used in the lens of M6.5, the bending parts 9a must enter the middle of the mounting surface 3h of the lens support 3 of the inner contour part 7a of the upper spring 7 and the arm part 7f of the upper spring 7. Therefore, under the width Wy of the existing bending part 9a, the gap between the coil 4 or the upper spring 7 and the lower spring 2 and each component needs to be reduced, so that interference among the components is easily caused, and the size of the magnet 6 or the gap between the components needs to be reduced. For the purpose that the lens 20 is converted into M6.5 from M6, the lens 20 must be reduced by 0.25 mm along the radial direction.
In order to prevent from generating interference among the components, the thickness Dc of the circular coil 4 in the radial needs to become into two layers from four layers, and thus the winding number is reduced, or the thickness Dy of the magnet yoke 9 is reduced, or the width Wy of the bending part is reduced. However, if the winding number is reduced, the total current passing through the flux is reduced, the pushing force is reduced, and thus similar characteristics do not exist, or if the thickness Dy of the magnet yoke 9 is reduced, the following failures may appear, namely the strength of the bending part 9a of the magnet yoke 9 is reduced, and the bending part 9a cannot serve as the clamping mechanism in the rotating direction to take effect.
Therefore, as shown in Patent Document 1, as a method in other rotating directions which is restricted by using the large-diameter lens (clamping mechanism in the rotating direction), the coil 4 formed in an octagonal shape is used. Or, if as shown in Patent Document 2, the magnet yoke 9 adopts an unbending structure.
The thickness of the clamping mechanism in the rotating direction of each component as shown in each patent document needs to be thinned and restricted to be minimum limit permitted by the large-diameter lens, under the condition that abnormal torque is applied to the rotating clamping part 3d or the rotating clamping part 11c, some rotating clamping parts 3d on the resin part side may be cracked, worn or deformed to cause damage or micro garbage. If the damage or micro garbage is generated, the durability of the rotating clamping parts 3d can be reduced, some problems may appear after the product is in the market, namely, the rotating clamping parts 3d can also be damaged even if under the conditions more relaxed than ordinary conditions, or the load exceeding allowable stress is applied to the upper spring 7 and the lower spring 2 to cause that the characteristics of the lens driving device 10 are worsened, or the damaged micro garbage is scattered everywhere to cause failure influence on the hysteresis characteristic during moving.
In the structure as shown in Patent Document 1, the bending part 9a of the magnet yoke 9 serves as a back yoke, and thus the bending part 9a enters the position near the middle of the coil 4, and whether the lens is damaged or not is unlikely to be discovered from the opening side of the lens 20. In the structure as shown in Patent Document 2, the rotating clamping part 3d is positioned on the lower side of the coil 4, and thus whether the lens is damaged or not is unlikely to be discovered from the opening part 11b of the lens 20 outside.
Therefore, in the existing rotation limiting method as shown in mentioned above, under the condition that the lens 20 is removed as the lens 20 is damaged or the abnormal rotating torque is applied due to impact, the clamping mechanism in the rotating direction is located near the middle (inner side) of the coil 4 or closer to the lower side than the coil 4, and thus each part is damaged by restricted rotation cannot be definitely confirmed from the opening part 11a. Moreover, under the condition that micro damage is caused, the parts cannot be confirmed to leave the factory directly, and it is predicted that troubles may appear after the parts are delivered to the destination (mobile terminal assembling destination) or the market.
Therefore, in the existing lens driving device 10, the upper spring 7 and the lower spring 2 may be deformed when being subjected to the torque (in the range of about 200-300 gfcm) greater than the existing torque, or the rotating clamping parts 3d, 11c serving as the clamping mechanisms in the rotating direction may be damaged. When the lens 20 is mounted or removed, in case of the condition that the rotating clamping parts 3d, 11c as the clamping mechanisms in the rotating direction are worn, shrunken or damaged or cause micro garbage, the damage or fragments can not be confirmed easily, and inferior-quality products can not be assigned reliably.